Presently, emergency vehicles, including ambulances, police vehicles, and emergency fire apparatus vehicles, output visible warning signals through the use of a beacon or a light bar mounted thereon, or via flashing strobe lights built into the body of the vehicle. A beacon ordinarily houses a continuous light source radiated by a rotating reflector, while a light bar typically contains a number of flashing (strobing) light sources or light sources radiated by rotating mirrors. A flashing strobe light built into the body of the vehicle is typically covered by a plastic lens or the like to increase its visibility and to achieve a specific color.
To ensure effectiveness, these lighting systems are required to meet certain performance specifications, such as those proposed by the Ambulance Manufacturers Division of the National Truck Equipment Association, AMD Standard 016. Another ambulance specification, General Services Administration Specification KKK-A-1822C, requires a minimum number of lights disposed at specific display locations on the vehicle and arranged to radiate the light in a certain manner.
With a beacon, a motorized driving mechanism rotates a parabolic reflector in order to alternately block and focus the light radiated to a given location so that the light appears to observers to be intermittent rather than continuous. The driving mechanism includes a relatively large motor, making such beacon systems rather inefficient. Beacons are also limited to flashing one color based on the color of the transparent housing surrounding the bulb and reflector.
With strobing bulbs, the desired intermittent light patterns are accomplished by repeatedly flashing one or more of the bulbs on and off. For example, in a light bar some of the lights are color-filtered so that observers can better differentiate between these emergency lights and the white and red lights of ordinary vehicles, and so that observers can distinguish among the different types of emergency vehicles. However, in order to display a variety of colors, a number of bulbs must be provided at different display locations in the light bar, each bulb radiating through its own colored glass or the like. Moreover, in addition to emergency lights, other lights may be added to an emergency vehicle. For example, an ambulance is typically outfitted with scene lights, also known as load lights, to continuously illuminate the area around the vehicle when parked to facilitate the loading of a person.
Although functional, light bars, strobe lights and rotating beacons have a number of additional drawbacks associated therewith. One drawback common to all three types of lights is that the bulbs often fail as a result of road-induced failures of the filaments therein due to shock and vibration. The high failure rate necessitates the frequent performance of time-consuming testing and maintenance procedures. The operating life of these conventional filament-based bulbs is typically on the order of 300 hours.
Consideration must also be given to the design and adaptation of vehicles for the subsequent installation of emergency lights. Significant mounting hardware and wiring is required to add light bars or beacons to a vehicle, or to build strobe lights into a vehicle, particularly when converting an otherwise standard vehicle to an emergency vehicle. Moreover, the mounting of either a beacon or a light bar onto the vehicle can result in a reduction in the vehicle's aerodynamics.
Another drawback that results from the mounting of light bars or beacons onto emergency vehicles is that the vehicles necessarily become more conspicuous, even at times when no emergency is present and the lights are not activated. This is undesirable in certain situations. By way of example, police officers often desire to have their police cars remain inconspicuous, such as when situating themselves to observe potential traffic offenders.
Finally, ambulances need to have a very stable, high-capacity power source so that the sensitive medical equipment present therein operates properly. However, flashing intermittent lights produce large, uneven power demands and can generate unpredictable electronic noise. Accordingly, ambulances having conventional flashing lights must be provided with a well-regulated, uninterruptible power source and adequate shielding, such as by adding electronic filtering and/or a completely separate power system. This increases the complexity and cost of the vehicle.